The present invention relates to radial support systems for refrigerated magnetic resonance magnets.
The economical operation of a refrigerated superconducting magnet requires that the heat load and hence the refrigeration load to the magnet windings be minimized. In cryostat systems which have a light weight, thin walled thermal shield cooled by a cryocooler, it is advantageous to support the thermal shield from the magnet cartridge. This allows the magnet cartridge and thermal shield to be assembled together prior to insertion in the vacuum vessel. The magnet cartridge, which is the primary mass within the enclosure, is independently supported by the vacuum vessel.
In order to minimize the conduction heat leak from the vacuum vessel and thermal shield to the magnet cartridge, it is necessary to use supports made with low thermal conductivity materials, minimized cross sectional area, and maximized length. The supports must be designed to minimize the deformation of the magnet cartridge and the thermal shield due to the reaction forces at the attachment points of the supports. The supports must permit the axial and radial positioning of the magnet cartridge and the thermal shield within the vacuum vessel. The adjustment mechanisms must be compatible with the overall cryostat assembly procedure.
During the cool down of the magnet from room temperature to operating temperature, there is normally a finite differential thermal contraction between the magnet cartridge, the thermal shield, and the outer vacuum vessel. The supports must accommodate this differential thermal contraction and maintain adequate support at operating temperatures.
The supports must be capable of withstanding the forces due to the dynamic shock loading of the system during shipping and handling. Shock loads during shipping have been measured at approximately 2 g vertical, and 1 g horizontal.
During the ramp up of a magnet during which the current in the windings is increased to their operating level, the magnet cartridge typically expands radially due to magnetic forces. There must be no frictional heating between the magnet cartridge and the supports during ramp up, as this could induce a local temperature rise in the magnet and lead to a magnet quench (transition from superconducting to normal resistance in the superconductive windings).
It is an object of the present invention to provide a radial support system to minimize heat input to the magnet cartridge while maintaining adequate mechanical strength and adjustment capability.